This invention relates to storm or emergency brakes for cranes. Specifically, the present invention relates to a fail-safe storm or emergency brake system for outdoor cranes, such as bridge, gantry, and portal cranes.
Large outdoor cranes, such as, for example, those employed in the logging industry, are often set up to move along a raceway, such as straight or curved rail, runway or other surface. The raceway may be, for example, a ballast and tie rail system, concrete slab rail or an elevated beam rail. A wheeled truck supports the leg(s) of the crane and moves across the runway. Cranes often employ two sets of legs connected by a structural girder arranged in a sawhorse configuration. Each leg of the girder may be driven bi-directionally along the runway, such as by motor driven wheels in the truck at the base of each leg. Alternatively, the crane may pivot about a center leg and an outer leg may move on a truck that rolls over an arc-shaped or circular surface.
The motion of these cranes along the runway may be slowed and ultimately stopped during normal operation of the crane by utilizing a standard braking system. The standard braking action may be accomplished by utilizing the regenerative capacity of the motors, such as by electrically slowing the motor to apply a retarding torque to the wheel gear box assembly in the truck, and thereby slow the crane. However, standard crane systems may not be suitable to slow or stop the crane during severe storm conditions or during other run-away situations caused by electrical or mechanical malfunctions.
High winds apply large forces to the crane. Strong winds may apply high loads to the cranes that often have great operational clearance heights and widths, such as on the order of heights of over one hundred feet (33 meters (m)) and widths of several hundred feet (such as greater than 100 m). The force applied by wind to the crane may cause the wheels of the truck to skid across the surface, even though the wheels are locked by the standard brake.
Cranes are top heavy and have the potential to overcome the braking and topple over, become twisted or become otherwise damaged if allowed to slide and move during high winds. Uncontrolled movements by the crane, such as may occur due to high winds, may damage the crane, the runway and surrounding areas. These uncontrolled crane movements may result in harm to personnel such as crane operators attempting to regain control over the crane and others in the vicinity while a crane topples.
To protect against damage and injury due to severe wind conditions occurring during non-operational periods, storm brakes in the trucks of the cranes engage the runway when wind forces overcome the braking action of the standard brakes and the wheels in the trucks slide across the runway. Storm brakes provide dynamic and emergency braking to stop and secure the crane. An example of storm brakes are disclosed in Canadian Published Patent Application 5,006,0/98 entitled “Storm Brake for Cranes.” Some storm brakes have brake shoe that move vertically downward and are rammed directly against the runway to achieve braking action. These ram-type brakes employ a brake shoe mounted on a piston that is moved hydraulically or pneumatically and mounted in a spring-set cylinder. The brake shoe is hydraulically or pneumatically moved downward and pressed against the runway.
The friction forces between the brake shoe and runway are greater than between the wheels and the runway. The larger friction forces of the brake shoe provide greater braking force between the truck and the runway than is achieved by braking just the wheels. Often the braking force is increased by causing the wheels come up from the raceway and thus increasing the load on the applied storm brake. The storm brakes when engaged hold the trucks and legs of the crane more securely to a single location on the runway than do the standard brakes alone.
However, hydraulic and pneumatic storm brake systems require maintenance and, at times, drip hydraulic fluid and compressor lubricants or antifreeze on the runway. Maintenance of these storm brake systems is consistent with large industrial hydraulic and pneumatic systems. These systems have pressurized fluid conduits that are prone to leakage and require regular inspection and periodic replacement of pressure components. The maintenance can be expensive in terms of the cost of repairs and in terms of lost crane productivity while the crane is immobilized for inspection and repair. In addition, the fluids in hydraulic and pneumatic storm brakes too often drip and are otherwise deposited on the runway. These fluids tend to be slippery and may cause the wheels on the girders to lose traction with the runway. The loss of traction in the wheels may result in sliding of the wheels and uncontrolled movements of the crane. Accordingly, there is a long felt need for a storm brake system that requires less maintenance than conventional hydraulic and pneumatic storm brake systems and does not deposit slippery fluids on the runway.